1. Field of the Invention
The present invention relates to an image pickup unit for endoscope including a solid-state image pickup device built in an insertion portion of an endoscope.
2. Description of the Related Art
In recent years, an endoscope has been used in a medical field and an industrial field. The endoscope can perform observation, treatment, and the like by inserting an elongated insertion portion into a tube with a small diameter. Reduction in the diameter of the insertion portion and shortening of a rigid portion are demanded in the endoscope in order to improve an insertion property.
In a so-called electronic endoscope including an image pickup unit for endoscope (hereinafter, abbreviated as an image pickup unit) built in a distal end portion of an insertion portion, the number of pixels of a solid-state image pickup device is increased, for example, in order to improve an observation performance.
In the image pickup unit, an objective lens unit and an image pickup device unit including the solid-state image pickup device are integrated. The image pickup device unit is an expensive unit among the units included in the endoscope.
The objective lens unit includes optical lenses that are a plurality of optical members, an interval ring, a diaphragm, and the like, which are fixed and installed in a lens frame.
On the other hand, the image pickup device unit mainly includes: a solid-state image pickup device (hereinafter, abbreviated as an image pickup device), such as a CCD and a C-MOS; a circuit substrate on which the image pickup device and various electronic components are mounted; and a plurality of signal lines connected to the circuit substrate.
The objective lens unit and the image pickup device unit are formed as an image pickup unit in which a lens frame forming the objective lens unit and a holding frame forming the image pickup device unit are integrated and fixed by bonding or joining.
Japanese Patent Application Laid-Open Publication No. 2009-273642 illustrates an image pickup unit for endoscope in which positioning of optical performance is facilitated to improve assembly work efficiency, and a waterproof and moisture barrier property is improved. In the image pickup unit for endoscope, a prism unit is provided with a first lens holding frame attachment portion and a second lens holding frame attachment portion in which optical axes are aligned.
Therefore, the first lens holding frame attachment portion is installed on a first lens unit, and the second lens holding frame attachment portion is installed on a second lens unit. As a result, the optical axes can be easily aligned, and the assembly work efficiency becomes excellent. Note that a holder tube of an image pickup device holder is fitted and fixed onto the second lens unit.
Japanese Patent Application Laid-Open Publication No. 2006-015076 illustrates an image pickup apparatus that allows reusing a component before exchange when an image pickup unit is repaired and exchanged. In the image pickup apparatus, a fixing member is used for fixation of a lens frame and a CCD holding frame. When the lens frame and the CCD holding frame are coupled, an adhesive or the like is not used for an attachment surface (fitting portion) coming into contact with both of a proximal end side outer circumference surface of the lens frame and a distal end side inner circumference surface of the CCD holding frame.
Note that it is assumed that a first frame member and a second frame member are respectively provided on a distal end side and a proximal end side across one frame member, and frame members are integrated and fixed by providing frame fixing portions based on joining or bonding. In this case, if a fitting area of a first frame fixing portion provided on the distal end side of the frame member and a fitting area of a second frame fixing portion provided on the proximal end side of the frame member are different, and a same adhesive is applied to respective fitting surfaces to provide the first frame fixing portion and the second frame fixing portion, the frame fixing portion with a small fitting area is broken up by a smaller load than the frame fixing portion with a large fitting area when a load is applied to break up the frame fixing portions.